feat: Discover docker ports as well

If processes are running in a container then the fwd process
can't read their internal FDs without the CAP_SYS_ADMIN property
which is equivalent to sudo. Even with sudo, I think you need to do
a lot of work to be able to read them -- spawning a process within
the cgroup, doing work there, and then communicating back.

This just uses the docker api to populate some default ports, which
later get overwritten if fwd can find a native process.

The Docker port scan takes about 1.5ms, and the full port scan takes
40+ms, so this adds basically no overhead.

Cargo.toml

@@ -15,6 +15,7 @@ bench = false
 
 [dependencies]
 anyhow = "1.0"
+bollard = "0.17.0"
 bytes = "1"
 copypasta = "0.10.1"
 crossterm = { version = "0.25", features = ["event-stream"] }